environment: fix bug introduced by commit a8409f4f1ac8

env_get_char is not a function, but a pointer to one.

Signed-off-by: Wolfgang Denk <wd@denx.de>

include/environment.h

@@ -107,8 +107,8 @@ typedef	struct environment_s {
 	unsigned char	data[ENV_SIZE]; /* Environment data		*/
 } env_t;
 
-/* Function that returns a character from the environment */
-unsigned char (*env_get_char)(int);
+/* Pointer to function that returns a character from the environment */
+extern unsigned char (*env_get_char)(int);
 
 /* Function that returns a pointer to a value from the environment */
 unsigned char *env_get_addr(int);